All experimental data contains insignificant information as well as useful information. The useful information is that from which the researcher learns an aspect of a studied object, such as a structure or composition. The insignificant information is that which the researcher wishes to unobtrusively discard without damaging essential information.
In particular, in the field of spectroscopy, the continuum contains background noise. As is known to those skilled in the art, numerical algorithms directed to background correction in spectroscopy have been developed. These methods include digital filtering, numerical derivatives, Fourier transforms, neural networks, genetic regression, wavelet transforms, principal component analysis (PCA), partial least squares (PLS), etc. These and other spectral background correction techniques are directed to the separation of an essential, material-specific portion of spectral information from its interfering part—the continuum background.
However, these known spectral background correction techniques are not adequate for all types of spectroscopy. In particular, some known background correction techniques are not robust with respect to spectrum shape and make poor background estimates when interfering lines are introduced into the spectral window. Other techniques do not compensate for the fluctuating background noise. Other techniques require prior knowledge of the analyte line position and spectrometer instrumental functions. Importantly, most known techniques require a reference spectra of pure elements to determine the positions of spectral lines and the underlying background.
The problem of background correction is particularly important in Laser Induced Breakdown Spectroscopy (LIBS) as spectra obtained in LIBS have poor reproducibility and, if a detector is not gated, high continuum background. The background can strongly vary from spectrum to spectrum and from sample to sample. Even for ablation from an ideal surface, small fluctuations in laser intensity can cause significant change in appearance of LIBS spectra. This effect is greatly multiplied for rough surfaces, surfaces that are not compositionally homogeneous, or for powders and aerosols. Adequate modeling of the background in LIBS is very important in order to improve its potential for both quantitative and qualitative analysis. Known methods of background correction do not adequately provide satisfactory background correction in LIBS.
Another technique that is frequently complicated by continuum backgrounds is Raman spectroscopy. Raman spectra contain a wealth of chemical and structural information about analyte systems, however, this information can be masked by background which overshadows inherently weak Raman signals.
The present invention overcomes the limitations of known background correction techniques in spectroscopy. In particular, the present invention is directed to approximation and automatic subtraction of continuum backgrounds obtained with non-gated detector systems in LIBS and Raman spectroscopy.